A preschool teacher in California admitted to slipping sleeping pills into the water cups of her ten preschool students; all of them are under two years of age. (Photo: Creative Commons)

Preschool teacher Debbie Gratz (Photo: Morgan Hill Police Department)

Sleeping pills in Sippy cups: A preschool teacher in Morgan Hill, Calif., was arrested Monday after admitting to authorities that she slipped sleeping pills into the Sippy cups of her toddlers.

ABC News reported that 59-year-old preschool teacher Debbie Gratz was witnessed putting something into the water cups of her ten students, all of whom are under the age of two. Morgan Hill Kiddie Academy said in a statement that the cups were confiscated before any children had contact with them and their contents dumped down the drain.

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Morgan Hill Police told ABC that a fellow employee at the preschool approached school officials last Friday after witnessing Gratz putting an unknown substance into the kids' Sippy cups. While Gratz was terminated that day, the police were not notified of the event until Monday. Collecting evidence proved difficult as the contents of the cups had already been disposed of. Investigators are concentrating on things like if parents or teachers have noticed any signs of excessive sleepiness or lethargy in their kids, according to KION.

After the witness reported the incident, school administrators confronted Gratz, who allegedly admitted to them that she had put Sominex, an over-the-counter sleep aid, into the Sippy cups of her students. Gratz has worked with children for about 20 years, KION reports.

Sominex contains diphenhydramine, which is an antihistamine. Adverse reactions from the drug can include drowsiness, dizziness, headache and paradoxical stimulation in children, which is when the drug has the opposite effect on the person than is intended.

Police investigators believe Gratz broke the pills up into smaller pieces. The police have said that they also believe this is not an isolated incident and that it has occurred before.

"We've contacted all 10 parents [of the children] that were under her care. We've received 30 to 35 phone calls, either past or present parents at the Kiddie Academy, so we're still trying to determine if this has been going on for some time," Morgan Hill Sgt. of Investigations Troy Hoefling told ABC News. "We don't think it's a one-time occurrence."

While Gratz admitted to putting sleeping pills in the kids' drinking cups, the preschool teacher has yet to comment on a motive. She has been charged with two counts of child endangerment and has been released. She is set to appear in court later this month, police announced.